The invention relates to a process for reducing the viscosity of compositions resulting from the polymerization of isocyanate monomers or from copolymerization of isocyanate monomers with another polymerizable compound, which generally have a high viscosity at room temperature, and for allowing the separation of the high-viscosity polymerization product from the corresponding isocyanate monomer.
During the preparation of oligomeric or polymeric compounds by polymerization of starting isocyanate monomers, or copolymerization with a compound other than an isocyanate, in particular a polyol, a resulting mixture is obtained which contains the desired oligomer or (pre)polymer and, predominantly, the unreacted monomer(s), which should be separated from the products of higher molar mass.
In particular, during the catalytic cyclotrimerization of isocyanate monomers, in particular of diisocyanate monomers, the resulting mixture contains the isocyanurate, polyisocyanate where appropriate, resulting from the condensation of at least three starting monomers, as well as unconverted monomers.
Now, one of the obstructions to the industrial preparation of (poly)isocyanurate polyisocyanates, in particular those obtained by catalytic cyclotrimerization of cycloaliphatic isocyanates, has up to the present been the separation of the unconverted monomer from the condensation products of higher mass.
The reason for this is that a large number of the compositions, in particular polyisocyanates, obtained after a catalytic (cyclo)trimerization reaction comprise polymerization products which have, at the separation temperatures usually used, a high viscosity or are even solid at these temperatures.
Thus, during the preparation of IPDT (isophorone diisocyanate trimer) which is obtained by catalytic cyclotrimerization of isophorone diisocyanate (IPDI or 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane), a mixture of polyisocyanates, in particular containing isocyanurate units, is obtained, which, in the purified state (IPDI content of less than 0.5%), is a solid whose melting point is about 110-115xc2x0 C. and in addition a non-newtonian fluid (viscosity at T greater than 115xc2x0 C. depends on the coefficient of shear). Separation of the IPDI from the crude trimerization mixture in the evaporators used for this purpose, in particular scraped-film evaporators, consequently requires the use of higher temperature levels than in the case of the separation of monomers of polymethylene diisocyanate type from the crude trimerization mixture obtained by polyaddition of these monomers.
In particular, in the final step of evaporation of the IPDIs, it is necessary to work at more than 200xc2x0 C. in order to remove all of the IPDI and to make the IPDT conveyable.
On an industrial scale, such operating conditions require adaptations which increase the duration and cost of the process: change of exchangers, accelerating pump on the IPDT before formulation, line plotting, etc.
In addition, the transportation of purified IPDT remains difficult on account of considerable losses of load, risks of blockage, difficulty in rinsing the lines, greater cross-contamination, etc.
Moreover, there is a need in the coating industry for low-viscosity polyisocyanate compositions which combine a certain number of properties often obtained only by using isocyanates of different nature.
Thus, EP 693,512 describes a polyurethane coating composition comprising a polyisocyanate component and a polyol component, the polyisocyanate component being obtained by mixing:
(A1) from 50 to 95% by weight of a 1,6-diisocyanatohexane-based polyisocyanate lacquer with a viscosity at 23xc2x0 C. of from 100 to 4000 mPa.s; and
(A2) from 5 to 50% by weight of a polyisocyanate containing isocyanurate groups, based on cycloaliphatic diisocyanates.
The polyisocyanate component can be obtained by adding, during the preparation of component A2, compound A1 to the crude reaction mixture at the end of the trimerization reaction and by then removing the excess cycloaliphatic monomers by thin-film distillation.
By virtue of the invention, it has been discovered, surprisingly, that by adding to an oligomer/polymer composition of high viscosity, obtained by polymerization, in particular catalytic (cyclo)trimerization, of starting isocyanate monomers, in particular of diisocyanates, or by copolymerization of these compounds with another polymerizable compound, an amount of less than 50% by weight of the monomer-free mixture of a product with a substantially lower viscosity than that of the high-viscosity oligomer/polymer composition, the viscosity of the polymer/oligomer composition can be reduced substantially, so as to allow separation by distillation (evaporation) of the high-viscosity oligomer or polymer from the unconverted isocyanate monomer(s) and to obtain this oligomer or polymer in high purity comprising less than 1%, preferably less than 0.5%, by weight of the corresponding unconverted isocyanate monomer(s).
In addition, the final compositions containing the mixture of oligomers/polymers of high and low viscosity in the proportions indicated have particularly advantageous application properties for the production of coatings, since some of its properties are better than those obtained with a simple mixture of the two types of polyisocyanate components in the same proportions.
For the purposes of the present invention, the expression high viscosity is intended to mean a viscosity generally of greater than 104 mPa.s at 25xc2x0 C., including compounds which are solid at 25xc2x0 C.
For the purposes of the present invention, the expression low viscosity is intended to mean a viscosity generally of less than 5xc3x97103 mPa.s at 25xc2x0 C. The viscosities are measured according to DIN standard 53019.
More generally, the ratio of the viscosities of the low-viscosity compound to the high-viscosity compound must be less than 1/1.5, preferably less than about 1/2.
The subject of the invention is thus a process for separating one (or more) oligomeric or polymeric compound(s) A obtained by polymerization or polycondensation of isocyanate monomers (A1) with each other or polymerization or polycondensation of isocyanate monomers (A1) with another copolymerizable monomer compound (A2), from the unconverted monomer(s), the said compound(s) A having, in the presence of an amount of monomers (A1 and optionally A2) of not more than 1% by weight, preferably not more than 0.5% by weight, a viscosity (a), this process comprising the following steps:
i) the viscosity of the crude polymerization or poly-condensation mixture containing the said compound(s) A is lowered by adding thereto one or more compound(s) B of viscosity (b) such that b/a is less than 1/1.5, and preferably less than 1/2, in an amount of less than 50% by weight of the mixture A plus B; and
ii) the mixture thus obtained is co-distilled so as to separate the compound(s) (A) and (B) from the unconverted monomers.
(A) and (B) are preferably miscible at the distillation temperature.
A2 is advantageously a polyfunctional monomer compound containing a labile hydrogen, in particular a polyol.
B2 is advantageously a polyfunctional monomer compound containing a labile hydrogen, in particular a monofunctional or polyfunctional alcohol.
(B) can be, in particular, a molecule with a boiling point, expressed in degrees Kelvin, at atmospheric pressure, which is substantially higher, advantageously by at least 20%, preferably by at least 30%, than the highest boiling point of A1 and A2.
(B) is advantageously an oligomeric or polymeric compound obtained by polymerization of isocyanate monomers (B1) or copolymerization of isocyanates (B1) with another polymerizable compound (B2).
(B) can also be a varnish or paint additive such as a xe2x80x9cmar-resistancexe2x80x9d agent, a spreading agent or a surfactant to help disperse A and B in aqueous media, or another additive used to give any property to a composition for preparing coatings.
The compounds A and B can also consist of a mixture of the compounds described above. In particular, A and B can comprise a mixture of polyisocyanates obtained by polymerization of identical or different monomers, and when they comprise copolymers, these can be obtained from mixtures of monomers and comonomers.
It is preferred to select A and B such that they do not react with each other, with the exception of the reactions which take place between the isocyanate functions which they bear, under the conditions of the process.
Advantageously, the molecular weight (Mw) of compound A is not greater than 3000, preferably than 2000 and more preferably than 1500.
Advantageously, the molecular weight (Mw) of compound B is not greater than 10,000, preferably than 5000 and more preferably than 2000.
The isocyanate functions in compounds (A) and (B) can also be totally or partly blocked with a blocking or masking group. Such a blocking or masking group will be selected such that it is not released at the distillation temperature of the (A)/(B) mixture.
An advantageous protecting group is a polyoxyalkylene group, in particular polyoxyethylene.
Advantageously, the low-viscosity compound (B), referred to as the viscosity-reducing product, is a polyisocyanate optionally containing isocyanurate unit(s), obtained by catalytic (cyclo)trimerization of isocyanate monomers or of a mixture of isocyanate monomers, optionally comprising carbamate, biuret, uretdione and/or allophanate groups. Preferably, (B) is the product of (cyclo)trimerization of an aliphatic isocyanate monomer containing a linear or branched alkylene chain, in particular of polymethylene diisocyanate, or of a mixture of aliphatic isocyanate monomers containing a linear alkylene chain with other polyisocyanate monomers, more particularly the isocyanurate polyisocyanate HDT (hexamethylene diisocyanate trimer) obtained by catalytic cyclotrimerization of hexamethylene diisocyanate (HDI), it being possible for the isocyanate function(s) to be temporarily blocked or otherwise.
Compound (B) can be added to the reaction mixture comprising (A) in purified form (at least 99% by weight of oligomers or polymers) or in crude form with the monomers B1 and, where appropriate, B2.
However, it is preferred to add the mixture containing monomers only if the conditions for distilling the monomers B1/B2 from A1/A2 are easy or when the percentage of monomers leaving the distillation is identical or only slightly different from that introduced for the polymerization, advantageously (cyclo)trimerization, reaction.
In general, it is preferred to use a compound (B) corresponding to the following general formulae: 
in which R1, which may be identical or different, represent H or an aliphatic hydrocarbon-based chain, preferably a linear C3-C20 alkylene chain, and X1 is chosen from: 
R1 being as defined above and Rxe2x80x21 is the aliphatic or cycloaliphatic hydroxycarbon-based residue of a polymer, in particular of a polyol, which is advantageously C3-C50, preferably C3-C30, optionally interrupted by one or more oxygen and/or sulphur atom(s) and optionally comprising aromatic and heterocyclic units in the chain and optionally one or more substituents, in particular arylene or alkyl groups, fluoro or silyl groups, etc.;
n is an integer between 1 and 7.
In general, it is preferred for (B) to represent a true polyisocyanate trimer. The expression xe2x80x9ctrue trimerxe2x80x9d is intended to mean an oligomer comprising an isocyanurate ring and only one, and constituting the product of theoretical cyclocondensation of three moles of isocyanate monomers, preferably diisocyanate monomers, it being possible for triisocyanates also to be suitable, with the exception of compounds originating from the condensation of more than four monomers and/or containing allophanate groups, as well as the oligomers containing isocyanurate units obtained by oligomerization of a polyisocyanate containing an isocyanurate unit.
It is generally preferred for the monomers B1, from which B is obtained, to be isocyanates, preferably diisocyanates or triisocyanates in which at least one, preferably two and, where appropriate, three of the carbon atoms bearing isocyanate functions are not secondary, tertiary or neopentyl carbon atoms.
The best results are obtained for monomers in which the hydrocarbon-based skeleton consists of a polymethylene sequence xe2x80x94(CH2)nxe2x80x94, n advantageously being between 2 and 10.
The oligomeric and/or polymeric compounds described in EP 524,500 and those described in FR 2,613,363 can be used in particular as compound (B).
A preferred compound B is the HDT corresponding to the formula 
in which R is xe2x80x94(CH2)6xe2x80x94.
HDT is a known product, obtained by catalytic cyclotrimerization of hexamethylene diisocyanate (HDI), which is fluid at room temperature and has a viscosity of about 2.5 Pa.s at 25xc2x0 C.
In addition, HDT is used in paint formulations in combination with IPDT at IPDT contents generally of less than 50% by weight.
Consequently, its addition during distillation phases does not cause any drawbacks since its presence in the final product is not only generally harmless, but can even be desirable.
The reason for this is that, as indicated above, it has been determined that the polyisocyanate (poly)isocyanurate mixtures obtained after the co-distillation process of the invention make it possible, by polycondensation with polyols, to obtain polyurethane coatings with remarkable and unexpected properties of strength and speed of drying of the films.
The NBDT (norbornane diisocyanate trimer)/HDT and IPDT/HDT and H12MDT/HDT mixtures or the mixtures of other diisocyanate trimers or dimers, of high viscosity, in particular cycloaliphatic ones, with diisocyanate dimers or trimers obtained by mixing and by co-distillation of the two respective compounds makes it possible subsequently to obtain, by polycondensation with polyols, polyurethane films which have properties equivalent to those of the polyurethane coatings obtained with co-trimers prepared by catalytic cyclotrimerization of the same cycloaliphatic diisocyanate monomers with hexamethylene diisocyanate.
Lysine triisocyanate compounds, which are virtually undistillable but represent good viscosity-reducing agents, including their monomer form, are also suitable for the purposes of the invention. They can also be used in partially condensed trimer form, i.e. in the form of the cyclotrimerization mixture comprising true trimers (containing an isocyanurate ring) mixed with the monomers and possibly the dimers (uretdione).
By virtue of the invention, any high-viscosity oligomer or polymer obtained by polymerization or poly-condensation of isocyanate monomers or of a mixture of isocyanate monomers, or copolymerization of isocyanate monomers with another copolymerizable compound, can be separated, by distillation, from the unconverted monomers, at temperatures which are compatible with an industrial process, including oligomers and polymers with a very high viscosity, of greater than 50 Pa.s at 25xc2x0 C., and products which are solid at room temperature.
In general, the best results are obtained:
when B comprises no hydrogen capable of forming a hydrogen bond; or
when B comprises a hydrogen atom capable of forming an intramolecular hydrogen bond (allophanates).
Compound (B) according to the invention can thus be used in particular to reduce the viscosity during the phases of distillation of the following high-viscosity polyisocyanates or mixture of polyisocyanates:
(poly)isocyanurate polyisocyanates, e.g. polymers containing at least one isocyanurate ring, obtained by polycondensation of aliphatic monomers, preferably containing a non-branched chain,
(poly)isocyanurate polyisocyanates comprising carbamate and/or allophanate groups,
polyisocyanates comprising biuret, carbamate and/or allophanate groups,
polyisocyanates comprising uretdione groups, and
polyisocyanate polyurethane prepolymers, obtained by condensation of isocyanate monomers, in particular diisocyanates, with a long-chain polyol, in particular the prepolymers of the type described in U.S. Pat. No. 5,115,071 obtained by polymerization of polyfunctional polyisocyanates comprising aromatic polyisocyanates such as toluene diisocyanate, tetramethylxylene diisocyanate and diphenylmethane diisocyanate; cycloaliphatic polyisocyanates such as cyclohexane diisocyanate, isophorone diisocyanate, norbornane diisocyanate or 2,5(6) -diisocyanatomethylbicyclo[2.2.1]heptane, NBDI), 1,3-bis(isocyanatomethyl)cyclohexane (1,3-BIC), dicyclohexylmethane diisocyanate or 4,4-dicyclohexylmethanediyl diisocyanate (H12MDI) and cyclohexyl 1,4-diisocyanate; and linear aliphatic polyisocyanates such as hexamethylene diisocyanate, with a polyol preferably having a functionality of greater than 2, more particularly between 2.2 and 4, and a weight-equivalent average weight of between 62 and 10,000, advantageously 62 and 5000, preferably 62 and 2000. Representative examples are trimethylolpropane, glycerol, pentaerythritol, dipentaerythritol, trihydroxybutane, ethylene glycol and partially alkoxylated adducts thereof, or polyisocyanate prepolymers comprising various urea, biuret, amide, ester, etc. functions.
These (poly)isocyanate compounds (A) correspond in particular to the following formulae: 
in which the groups R2, which may be identical or different, are chosen from an aliphatic, cycloaliphatic or aromatic hydrocarbon-based chain preferably comprising from 2 to 50 atoms, preferably from 2 to 20 carbon atoms, the aliphatic or cycloaliphatic chains optionally being substituted with or interrupted by one or more, preferably C4-C8, arylene groups,
Rxe2x80x22 is the hydrocarbon-based residue generally of a polymer, in particular of a polyol, which is preferably C3-C50, optionally interrupted by one or more oxygen and/or sulphur atom(s) and optionally comprising aromatic and heterocyclic units in the chain and one or more substituents, in particular arylene or alkyl groups, or fluoro or silyl groups, etc.; n is an integer between 1 and 7,
and X is a group chosen from 
R2 and Rxe2x80x22 being as defined above.
The high-viscosity compound (A) is advantageously a polyisocyanate isocyanurate or biuret obtained by catalytic (cyclo)trimerization of cycloaliphatic diisocyanates, preferably IPDT, NBDT, H12MDT or 1,3-BDT (1,3-BIC trimer) or of branched aliphatic diisocyanates, for example MPDT (2-methylpentamethylene diisocyanate trimer).
Compound (B) is added to the crude polymerization mixture in a compound (B)/compound (A) weight ratio of between 5/95 and 49/51, preferably between 5/95 and 45/55.
The viscosity-reducing compound (B) can be added to the crude mixture obtained after the polymerization reaction of the starting isocyanate monomers with each other and/or with another compound, in particular a polyol as defined above, directly in the polymerization reactor, or can be added to the resulting crude mixture by in-line mixing before admission into the distillation train, in order then to be co-distilled with the high-viscosity oligomer or polymer which it is desired to separate from the unconverted monomer(s).
The co-distillation temperature is advantageously in the range between 120 and 250xc2x0 C., preferably between 150xc2x0 C. and 210xc2x0 C.
A subject of the invention is also the use of one (or more) oligomeric or polymeric compound(s) (B) of viscosity (b) obtained by polymerization of isocyanate monomers or copolymerization of isocyanate monomers with another polymerizable compound, for the separation of an oligomeric or polymeric compound (A) of viscosity (a), obtained by polymerization of isocyanate monomers or copolymerization of isocyanate monomers with another polymerizable compound, from the corresponding isocyanate monomers, by co-distillation of the said compound(s) (B) and (A), the ratio of the viscosities b/a being less than 1/1.5, preferably less than 1/2, and the amount by weight of compound (B) relative to the mixture (A) and (B) being less than 50%.
A subject of the invention is also a polyisocyanate composition containing one or more isocyanurate functions, comprising:
from 51 to 95% by weight of a first polyisocyanate obtained by (cyclo)trimerization of isocyanate monomers, and optionally another copolymerizable monomer,
from 5 to 49% by weight of a second polyisocyanate obtained by (cyclo)trimerization of isocyanate monomers, and optionally another copolymerizable monomer, in which the ratio of the viscosities of the second polyisocyanate to the first polyisocyanate is less than 1/1.5, preferably less than 1/2, the said composition being obtained by co-distillation of the said first polyisocyanate and of the said second polyisocyanate and being characterized in particular by the presence, in the composition obtained after the distillation, of traces of mixed compounds of the said first polyisocyanate and of the said second polyisocyanate linked by dimeric bridging.
The isocyanate monomers are advantageously diisocyanates or triisocyanates, diisocyanates being preferred.
These compositions make it possible to obtain polyurethane films with excellent properties of mechanical strength and of resistance to bad weather, at the same time as excellent film-drying properties.
The polyisocyanates obtained by the process of the invention are advantageously used as hardeners for the preparation of coatings, in particular polyurethane paints and varnishes, by reacting polyisocyanates with a polyol.
To this end, any type of polyol is suitable.
However, it has been found, surprisingly, that certain polyols provide appreciable advantages when they are reacted with polyisocyanates obtained in accordance with the present invention.
These polyols can be of acrylic or polyester nature.
When a polyol of acrylic nature is used, it is preferred for this polyol to satisfy the following conditions for a solids content (SC) of between 75-80% by weight.
Mw (weight-average molecular weight) not greater than 10,000, advantageously not greater than 5000, preferably not greater than 2000.
Mw is preferably less than 10,0000, advantageously less than 5000, preferably less than 2000.
Mn (number-average molecular weight) not greater than 5000, advantageously not greater than 3000, preferably not greater than 800.
Mn is preferably less than 5000, advantageously less than 3000, preferably less than 800.
Mw/Mn (dispersity ratio) not greater than 5, advantageously not greater than 3, preferably not greater than 2.
Mw/Mn is preferably less than 5, advantageously less than 3, preferably less than 2.
number of OH/molecule greater than or equal to 2, advantageously greater than 2.
For further details, reference may be made to ASTM standard E222.
The Mn and Mw values are advantageously obtained by gel permeation exclusion chromatography taking styrene as standard.
Polyols obtained by polymerization of hydroxyalkyl(meth)acrylates, in particular hydroxyethyl (meth)acrylate and hydroxypropyl (meth)acrylates, are preferred.
The resins sold under the names Joncryl SCX 922 (Johnson Polymers) and Synocure 866 SD (Cray Valley) are most particularly preferred.
When the polyols are of polyester nature, the ones preferred are those with a 100% SC and a viscosity of not greater than 10,000 mPa.s, advantageously not greater than 5000 mPa.s, preferably not greater than 1000 Pa.s, whose Mw is generally between 250 and 8000.
In order to obtain a satisfactory viscosity, it is also possible to add a reactive solvent to the polyol before or after mixing with the polyisocyanate.
Advantageously, an amount of reactive diluent of not greater than 30%, advantageously not greater than 20%, preferably not greater than 10%, by mass relative to the dry mass of the polyol is used.
Considerable advantages in terms of properties of the final coating are already obtained for an amount of reactive solvent of less than 10% by weight. These properties, in particular the speed of drying, the hardness of the coating and the impact strength are also excellent when the amount of reactive solvent is lowered, which includes the absence of reactive solvent.
Another subject of the invention consists of the compositions for simultaneous or successive application, comprising:
a polyisocyanate composition obtained by the process of the invention, and
a polyol as defined above.
The compositions obtained by the process of the invention can be used in particular in aqueous coating formulations, by being placed in suspension, in emulsion or in dispersion, or dissolved by grafting hydrophilic agents or by addition of surfactant compounds.
The compositions of the invention can undergo a reaction of partial or complete temporary masking of the isocyanate functions with one or a mixture of masking agents.
The isocyanate functions can then be restored by applying a physicochemical process such as increasing the temperature, or can be converted or polymerized by applying a physicochemical process such as ultraviolet radiation.
The compositions according to the invention can also be in the form of suspensions.
They can comprise, besides the components described above:
optionally one or more inorganic or organic compound(s) with a pigmentation or filler function, a matt-effect agent or any other additive intended to facilitate the application of the coating or to improve the properties of the coating, such as, for example, a spreading agent, a xe2x80x9ccicatrizingxe2x80x9d agent, etc.,
optionally one or more catalysts,
optionally one or more surface agents to improve the use of the formulation, such as, for example, an agent with a surfactant property, an anti-foaming agent, a solvent, an aqueous solution whose pH is optionally adjusted.
The examples below illustrate the invention.